Add better error message for partial move

src/librustc_mir/borrow_check/error_reporting.rs

@@ -130,6 +130,11 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
             );
 
             let mut is_loop_move = false;
+            let is_partial_move = move_site_vec.iter().any(|move_site| {
+                let move_out = self.move_data.moves[(*move_site).moi];
+                let moved_place = &self.move_data.move_paths[move_out.path].place;
+                used_place != moved_place && used_place.is_prefix_of(moved_place)
+            });
             for move_site in &move_site_vec {
                 let move_out = self.move_data.moves[(*move_site).moi];
                 let moved_place = &self.move_data.move_paths[move_out.path].place;
@@ -175,8 +180,9 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                 err.span_label(
                     span,
                     format!(
-                        "value {} here after move",
-                        desired_action.as_verb_in_past_tense()
+                        "value {} here {}",
+                        desired_action.as_verb_in_past_tense(),
+                        if is_partial_move { "after partial move" } else { "after move" },
                     ),
                 );
             }

src/test/ui/borrowck/borrowck-uninit-field-access.ast.nll.stderr

@@ -20,7 +20,7 @@ error[E0382]: use of moved value: `line2`
 LL |     let _moved = (line2.origin, line2.middle);
    |                                 ------------ value moved here
 LL |     line2.consume(); //[ast]~ ERROR use of partially moved value: `line2` [E0382]
-   |     ^^^^^ value used here after move
+   |     ^^^^^ value used here after partial move
    |
    = note: move occurs because `line2.middle` has type `Point`, which does not implement the `Copy` trait
 

src/test/ui/borrowck/borrowck-uninit-field-access.mir.stderr

@@ -20,7 +20,7 @@ error[E0382]: use of moved value: `line2`
 LL |     let _moved = (line2.origin, line2.middle);
    |                                 ------------ value moved here
 LL |     line2.consume(); //[ast]~ ERROR use of partially moved value: `line2` [E0382]
-   |     ^^^^^ value used here after move
+   |     ^^^^^ value used here after partial move
    |
    = note: move occurs because `line2.middle` has type `Point`, which does not implement the `Copy` trait
 

src/test/ui/moves/moves-based-on-type-cyclic-types-issue-4821.nll.stderr

@@ -5,7 +5,7 @@ LL |         Some(right) => consume(right),
    |              ----- value moved here
 ...
 LL |     consume(node) + r //~ ERROR use of partially moved value: `node`
-   |             ^^^^ value used here after move
+   |             ^^^^ value used here after partial move
    |
    = note: move occurs because value has type `std::boxed::Box<List>`, which does not implement the `Copy` trait
 

src/test/ui/moves/moves-based-on-type-match-bindings.nll.stderr

@@ -5,7 +5,7 @@ LL |         Foo {f} => {}
    |              - value moved here
 ...
 LL |     touch(&x); //~ ERROR use of partially moved value: `x`
-   |           ^^ value borrowed here after move
+   |           ^^ value borrowed here after partial move
    |
    = note: move occurs because `x.f` has type `std::string::String`, which does not implement the `Copy` trait
 

src/test/ui/nll/move-subpaths-moves-root.stderr

@@ -4,7 +4,7 @@ error[E0382]: use of moved value: `x`
 LL |     drop(x.0);
    |          --- value moved here
 LL |     drop(x); //~ ERROR use of moved value
-   |          ^ value used here after move
+   |          ^ value used here after partial move
    |
    = note: move occurs because `x.0` has type `std::vec::Vec<i32>`, which does not implement the `Copy` trait
 

src/test/ui/ref-suggestion.nll.stderr

@@ -25,7 +25,7 @@ LL |         (Some(y), ()) => {},
    |               - value moved here
 ...
 LL |     x; //~ ERROR use of partially moved value
-   |     ^ value used here after move
+   |     ^ value used here after partial move
    |
    = note: move occurs because value has type `std::vec::Vec<i32>`, which does not implement the `Copy` trait
 

src/test/ui/unsized-locals/borrow-after-move.nll.stderr

@@ -5,7 +5,7 @@ LL |         let y = *x;
    |                 -- value moved here
 LL |         drop_unsized(y);
 LL |         println!("{}", &x);
-   |                        ^^ value borrowed here after move
+   |                        ^^ value borrowed here after partial move
    |
    = note: move occurs because `*x` has type `str`, which does not implement the `Copy` trait
 
@@ -27,7 +27,7 @@ LL |         let y = *x;
    |                 -- value moved here
 LL |         y.foo();
 LL |         println!("{}", &x);
-   |                        ^^ value borrowed here after move
+   |                        ^^ value borrowed here after partial move
    |
    = note: move occurs because `*x` has type `str`, which does not implement the `Copy` trait
 
@@ -48,7 +48,7 @@ error[E0382]: borrow of moved value: `x`
 LL |         x.foo();
    |         - value moved here
 LL |         println!("{}", &x);
-   |                        ^^ value borrowed here after move
+   |                        ^^ value borrowed here after partial move
    |
    = note: move occurs because `*x` has type `str`, which does not implement the `Copy` trait
 

src/test/ui/unsized-locals/double-move.nll.stderr

@@ -14,7 +14,7 @@ error[E0382]: use of moved value: `x`
 LL |         let _y = *x;
    |                  -- value moved here
 LL |         drop_unsized(x); //~ERROR use of moved value
-   |                      ^ value used here after move
+   |                      ^ value used here after partial move
    |
    = note: move occurs because `*x` has type `str`, which does not implement the `Copy` trait